The invention relates to the cutting of continuous filamentary tow into staple lengths, and in particular to the high speed cutting of crimped or uncrimped tow into lengths of 3/4 inch or shorter.
Cutters have been heretofore proposed for cutting a continuous filamentary tow of man-made fiber, such as polyester, for example, into staple lengths. Exemplary of such proposals are the disclosures of U.S. Pat. No. 3,485,120 issued to Keith on Dec. 23, 1969, U.S. Pat. No. 3,831,481 issued to Van Doorn et al on Aug. 27, 1974, and U.S. Pat. No. 3,733,945 issued to Cook on May 22, 1973.
In the Keith patent, for example, there is disclosed a cutter wheel which comprises a pair of interconnected upper and lower circular plates which are spaced in the direction of the axis of rotation of the wheel. The wheel is provided with a circular array of cutter blades which have sharpened edges and are oriented parallel to the axis of rotation and facing radially outwardly. The spacing between adjacent cutting edges corresponds to the desired length of cut of the tow. Each blade is mounted to a support post, the posts having their ends connected to the plates and thereby serving to interconnect the plates. The posts provide substantially all of the resistance to separation of the plates in the radial and axial directions. The upper plate is rotatably driven, with rotary motion being transmitted therefrom to the lower plate primarily by the support posts. As the reel is rotated, a continuous-length tow is wrapped around the periphery of the cutting edges of the blades. As the radial thickness of the two builds-up, a pressure roller presses the tow radially inwardly past the blades so that the tow is served into the desired lengths. The severed tow fibers pass into the wheel and exit via a center opening in the lower plate.
In the Van Doorn et al patent it is proposed to interconnect the plates by means of a plurality of posts that are spaced radially inwardly of the blades from between 1/8 inch to 1-1/2 inch. There are fewer posts provided than the number of blades. The sides of each post is divergent in a radially inward direction to define a generally wedge-shaped post.
It has been proposed in Spaller U.S. Pat. No. 3,777,610 issued Dec. 11, 1973 to interconnect the upper and lower plates solely by means of the blades themselves (i.e., omit the support posts). However, in such an arrangement the blades would be unable to resist the substantial axial forces which tend to separate the plates in the axial direction, unless substantially reinforced. Such reinforcement, however, could unduly complicate individual removal and replacement of the blades.
While cutting wheels of the type illustrated in the Van Doorn et al and Keith patents have performed acceptably when cutting tow into lengths longer than about 1/2 inch, problems have been encountered when attempting to cut uncrimped tow into lengths less than 1/2 inch. It has been found that the cut fibers tend to "pack" within the the cutter wheel. Eventually, the packed fibers build-up to such an extent that the wheel becomes clogged and further cutting is rendered impossible. Accordingly, the cutter must be shut down and the clog removed. Such a problem has been experienced at low throughput speeds and to a greater extent at high throughput speeds (e.g., at or greater than 450 fpm tow velocity). One cause of this problem is the obstruction to fiber flow which is presented by support posts which extend beyond the sides of the blades and into the fiber throughflow passages. Unless the rotary speed of the cutter wheel is slowed, there may result a complete blockage of the throughflow passages and/or a mutual separation of the plates in the axial direction. Furthermore, the radial forces which must be exerted upon the fibers by the pressure rollers is increased, thereby accelerating the rate of wear of the cutting edges. Such wear results in a greater amount of broken ends occurring on the cut tow, thereby adversely affecting quality.
In copending application Ser. Nos. 343,241 and 343,242 of Waite et al and Glick, respectively, each filed Jan. 27, 1982, it has been proposed to cut the tow while wet and to interconnect the upper and lower plates by means of connector arms which define a clearance inwardly of the blade to accommodate free inward travel of the tow. As a result, the tow is cut with less change of flow blockage and at high throughput speeds. Notwithstanding the improved cutting performance resulting from these proposals, room for further improvement remains, especially in the area of resisting the axial forces which tend to mutually separate the plates.